Data from the Kaiser-Permanente Births Defects Study, a large prospective study of pregnancy outcomes, are being used to evaluate differences in the birth weights and gestational ages of babies born to women of different ethnic groups. The ethnic groups included in this study were Whites, Hispanics, Blacks, Asians, and others. Univariate and multivariate analyses of the effects of a large number of variables are being done to determine if the differences in birth weight between the four ethnic groups can be explained. Preliminary analyses show that after controlling for smoking, alcohol, and seven other variables, large differences in birth weight persist between Blacks and Whites and Asians and Whites. The babies of Black women and Asian women are on average about 200 grams lighter than babies of White women. Black women also have about two times the incidence of preterm deliveries compared to White women.